Both the three-axis machine and the five-axis machine need to be equipped with an automatic pallet changer (APC) in order to improve the processing efficiency. The APC comprises a rotary stage capable of quickly replacing the workpiece by its rotation mechanism. The rotary stage usually comprises a fixed axle and a rotation axle. A bearing is disposed between the fixed axle and the rotation axle in order to reduce the friction between them, thereby improving the stability of the rotary stage and reducing its abrasion. Nonetheless, when the workpiece is not evenly distributed on the rotary stage, the rotary stage in rotation shakes because the bearing of the rotary stage is uneven.
Therefore, it is important to solve the problem caused by uneven weight distribution of the work piece on the rotary stage because this may improve the stability and the durability of the rotary stage.